For car makers attempting to integrate its digital Car Keys software, Apple has developed a testing app (via 9to5Mac).

By placing an iPhone or Apple Watch next to the driver-side door, customers may unlock and start a compatible vehicle with Apple’s digital car key function. The Wallet app stores the auto keys similar to a credit card. Only specific BMW, Kia, and Genesis automobiles can use the feature.
The new “Car Keys Testing” app, which Apple launched in July 2022, enables authorized MFi developers to test and confirm their digital car keys technology integration.

According to Apple, the developer tool is as follows:
Exclusively for usage by MFi Licensees. Use the Car Keys Tests app to test and confirm the connectivity, functionality, and other essential requirements for the certification process of the automobiles you design that incorporates Apple digital car keys technology.
A direct link exists to see and download “Car Keys Testing,” even if it isn’t accessible through the App Store. Nevertheless, to proceed past the login screen, developers must have MFi licenses.

